Diesel powered vehicles may have advantages over spark ignited engines. For example, diesel engines may have reduced pumping losses and higher efficiency as compared to spark ignition engines. However, diesel engines are often operated with high intake manifold pressures to improve engine efficiency. Consequently, there may be fewer opportunities for a diesel engine to provide vacuum to operate vehicle systems that are assisted or powered via vacuum. One way for a diesel engine to provide vacuum to vehicle systems is to mechanically couple a vacuum pump to the diesel engine. As the engine rotates, the vacuum pump generates vacuum and evacuates a vacuum reservoir. Nevertheless, at lower engine speeds, such as idle speeds, the vacuum pump may not generate sufficient vacuum to operate some vacuum operated systems. Therefore, the vacuum operated systems may not perform as is desired. For example, if a diesel engine is idling and a driver repeatedly applies and releases vehicle brakes, the driver may notice undesirable hard brake pedal feel (e.g., increased resistance to brake application by the driver). The hard brake pedal feel may be a result of less than a desired amount of vacuum being available to operate the vehicle brakes.
The inventor herein has recognized the above-mentioned issue and has developed an engine method, comprising: increasing a speed of a vacuum pump via increasing engine idle speed when an engine is idling in response to a request to increase an amount of stored vacuum.
By increasing an engine idle speed in response to a request to increase an amount of stored vacuum, it may be possible to provide the technical result of increasing an amount of vacuum produced via a mechanical vacuum pump coupled to a diesel engine during engine idle conditions. For example, an engine may be controlled to a base engine idle speed when a driver has not applied an accelerator pedal. The base engine idle speed may be a speed that conserves fuel and is a speed less than a speed where a torque converter transfers more than a threshold amount of torque. However, a vacuum pump coupled to the engine may make less vacuum than is desired at the base engine idle speed. By increasing engine idle speed to a speed greater than base idle speed, the vacuum pump may increase its vacuum output, thereby improving operation of the vehicle's vacuum operated systems.
The present description may provide several advantages. Specifically, the approach may improve operation of a vehicle's vacuum operated systems. Additionally, the approach may not increase engine fuel consumption much of the time since the approach may only be applied during selected engine operating conditions that may not be frequently encountered. Further, the approach may compensate for vacuum generation at ambient conditions that may reduce or increase the rate of vacuum generation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.